Ethylbenzene is a valuable product that is used mainly for the manufacture of styrene monomer. Most ethylbenzene is produced by alkylation of benzene with ethylene. A byproduct also produced is polyethylbenzene. Therefore, ethylbenzene production processes contain two reaction sections, alkylation and transalkylation. The polyethylbenzenes produced from minor side reactions are recycled back to the transalkylation section and reacted with benzenes to produce more ethylbenzene. The alkylator and transalkylator effluents undergo separation operations to separate recycle benzene, ethylbenzene product, recycle polyethylbenzene and by-product streams using distillations. Traditionally three distillation columns are used. The first is typically a benzene column, used to recover excess benzene from the reactor effluents. The benzene column overhead, which is largely benzene, is typically recycled to the alkylator and transalkylator. The second distillation column is typically an ethylbenzene column used to recover the ethylbenzene product from the benzene column net bottoms. The ethylbenzene product is recovered as overhead, typically the net overhead, from the ethylbenzene column. The ethylbenzene product may be routed directly as feedstock to a styrene processes unit, or may be sent to storage. The third distillation column is usually a polyethylbenzene column used to recover recycle polyethylbenzene from the ethylbenzene column bottoms stream. Polyethylbenzene is recovered in the overhead of the polyethylbenzene column and is typically recycled to the transalkylator. The high boiling bottoms, flux oil, is usually cooled and sent to storage. Optionally, a fourth column, a light ends column, may be used to remove a small amount of light ends, light non-aromatics, and water from the recycle benzene stream.
The present invention provides an improvement over current process flow schemes by replacing the benzene column and the ethylbenzene column with a single divided wall column. The resulting advantages include a savings in the HP steam used in the reboilers, a savings in condenser duty, a capital costs savings due to a reduction in equipment count and heat exchanger surface area, and a higher ethylbenzene recovery. Additional advantages include a reduction in plot space required, lower flare equipment, and less hydrocarbon inventory which can have a safety advantage.
The dividing wall or Petyluk configuration for fractionation columns was initially introduced some 50 years ago by Petyluk et al. A recent commercialization of a fractionation column employing this technique prompted more recent investigations as described in the article appearing at page s14 of a Supplement to The Chemical Engineer, 27 Aug. 1992.
The use of dividing wall columns in the separation of hydrocarbons is also described in the patent literature. For instance, U.S. Pat. No. 2,471,134 issued to R. O. Wright describes the use of a dividing wall column in the separation of light hydrocarbons ranging from methane to butane. U.S. Pat. No. 4,230,533 issued to V. A. Giroux describes a control system for a dividing wall column and illustrates the use of the claimed invention in the separation of aromatics comprising benzene, toluene and orthoxylene.
Using a dividing wall column in the present invention provides significant advantages over ethylbenzene production processes that do not employ a dividing wall fractionation column, as is shown below.